//Given a binary search tree (BST), find the lowest common ancestor (LCA) of two
// given nodes in the BST. 
//
// According to the definition of LCA on Wikipedia: “The lowest common ancestor 
//is defined between two nodes p and q as the lowest node in T that has both p and
// q as descendants (where we allow a node to be a descendant of itself).” 
//
// 
// Example 1: 
//
// 
//Input: root = [6,2,8,0,4,7,9,null,null,3,5], p = 2, q = 8
//Output: 6
//Explanation: The LCA of nodes 2 and 8 is 6.
// 
//
// Example 2: 
//
// 
//Input: root = [6,2,8,0,4,7,9,null,null,3,5], p = 2, q = 4
//Output: 2
//Explanation: The LCA of nodes 2 and 4 is 2, since a node can be a descendant o
//f itself according to the LCA definition.
// 
//
// Example 3: 
//
// 
//Input: root = [2,1], p = 2, q = 1
//Output: 2
// 
//
// 
// Constraints: 
//
// 
// The number of nodes in the tree is in the range [2, 105]. 
// -109 <= Node.val <= 109 
// All Node.val are unique. 
// p != q 
// p and q will exist in the BST. 
// 
// Related Topics 树 深度优先搜索 二叉搜索树 二叉树 
// 👍 670 👎 0


package leetcode.editor.cn;

//Java：Lowest Common Ancestor of a Binary Search Tree
class P235LowestCommonAncestorOfABinarySearchTree {
    public static void main(String[] args) {
        Solution solution = new P235LowestCommonAncestorOfABinarySearchTree().new Solution();
        // TO TEST
    }
    //leetcode submit region begin(Prohibit modification and deletion)

    /**
     * Definition for a binary tree node.
     * public class TreeNode {
     * int val;
     * TreeNode left;
     * TreeNode right;
     * TreeNode(int x) { val = x; }
     * }
     */

    class Solution {
        public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
            if (root == null) {
                return null;
            }
            if (root.val == p.val || root.val == q.val) {
                return root;
            }
            TreeNode left = lowestCommonAncestor(root.left, p, q);
            TreeNode right = lowestCommonAncestor(root.right, p, q);
            if (left != null && right != null) {
                return root;
            } else {
                return left == null ? right : left;
            }

        }

    }
//leetcode submit region end(Prohibit modification and deletion)

}